1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Background Art
In recent years, the damascene process has been used to form the interconnects of semiconductor devices. According to the damascene process, recessed portions that are grooves or holes are formed in the surface of an insulating film in advance, and the recessed portions are filled with Cu. The unnecessary portions of Cu are then removed by chemical mechanical polishing (CMP), to form the interconnects.
To bury Cu according to the damascene process, a plating technique is normally used. In a case where Cu is buried in the recessed portions by electrolytic plating, a seed film is formed to supply current at the time of the electrolytic plating.
If the recessed portions are very fine, however, the seed film blocks the upper portions of the recessed portions, so that the plating solution does not reach sufficiently depth in the recessed portions. As a result, defects may be formed in the plating film. Therefore, thinner seed films are being developed.
A seed film is formed by processing performed in vacuum. However, being exposed to the atmosphere prior to electrolytic plating, the seed film might be oxidized by oxygen or moisture or the like existing in the atmosphere. The oxide formed through the oxidation is dissolved in a plating solution. Therefore, once a thinned seed film is oxidized, the resultant oxide is dissolved in a plating solution, so that the seed film disappears at some locations. As a result, defects are formed, and degradation of electrical reliability, such as defective via connections, might be caused.
A technique for forming a sacrifice seed film of Cu on a seed film containing Ru, Ir, or both Ru and Ir has been disclosed (see JP-A 2007-150298 (KOKAI), for example). This sacrifice seed film, however, is made of Cu or a Cu alloy. Therefore, oxygen permeates the sacrifice seed film, so that the seed film might be oxidized.